Of course straps can work fine. You totally underestimate how strong a strap can be made and how well it can secure something down. If turbulence is to the point where a reinforced strap gets snapped then the plane's probably fucked anyway. We're talking nice firm, chunky straps well anchored to a fixed point that wrap around solid parts of the wheelchair. We're not talking zip ties found in uncle Frank's garage on the bottom shelf.
Now, if the strap is fastened around a sharp edge of the chair, that's a problem, but a strap can be affixed to various points around a chair, and if a chair is, for whatever reason, outright incompatible with the system, will then shit happens and that dude can't fly, which is no different to had they disallowed wheelchairs in the first place. Something is better than nothing, right?
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Lol, you're salty about all those privileges? Dude, you don't realise how privileged you are (if you're not disabled). Pretty sure people out there with no freaking legs would think you're the lucky one. If I seriously ask you now, would you willingly have your legs made useless or removed to gain those benefits, would you say yes? If not, then shut up
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Well I checked out your picture and I saw 2 seats. One regular sized seat, and one double-sized seat that could seat 2 people (or 1 large person). A large seat that can sit 2 is still technically one seat, just a... big seat. (But this has derailed into semantics and I'm not helping either!)